1. Field of the Invention
Optical systems are becoming more and more widely used for signal transmission lines, particularly for digital transmission of data bits in telephone systems, data transmission systems, and the like. In many ways, optical fibers have capabilities which far exceed those of electrical wiring. When used for connecting components in optical transmission systems in a small space, a rather significant problem can arise with the optical fibers. Specifically, the optical fibers have a minimum bend radius which will still permit effective data transmission without signal attenuation or loss, and depending upon the diameter of the fiber and the material from which the fiber is made, the minimum effective bend radius may be so great as to cause difficulties in producing small package connection. This is also true in the case of bundled fibers.
Because of the mechanical and optical limitations, a strand of optical fiber can only be bent in gradual curves with a radius of at least about 2 centimeters. But with more and more use of fiber optics, this problem becomes more and more significant, since designers of devices incorporating fiber optics are less willing to allow for such curves at the expense of decreasing the efficiency of the design.
Bent optical fibers have application in numerous fields such as oil well logging cable and light pipes for sensing in hazardous environments such as nuclear reactors, as well as in telephone transmission systems and many other applications. Such fibers are also snugly positioned in connectors of a variety of types, just as with wire conductors.
In connection with the bending of an optical fiber at a sharp angle, two primary problems arise. The first is that in bending the fiber at a short radius, the fiber is likely to be stressed too greatly so as to cause internal fractures. The second problem is that of keeping light from exiting the fiber at the apex of the bend. Internal fractions can cause diffusion, distortion or attenuation of the transmitted light signal, and the light would often exit the fiber if the bend was sharper than the sum of the critical angle of the particular type of fiber and the angle of the beam of light relative to the wall of the fiber. In bundles of fibers, the problems may arise in some of the fibers in the bundle and not in others, and to different extents.
2. Description of Related Art
Very little prior art has dealt with these problems, except to recognize that they exist in order to avoid the need to bend the fibers. U.S. Pat. No. 1,981,999 to French, dated Nov. 27, 1934, discloses an optical telephone system, in which light cables may be bent at an angle and provided with a mirror at the bend to change the direction of the light. The mirror may be curved such spherical or parabolic, or it may be flat. Further, the light cable may be provided with two such bends and mirrors. However, the patent provides no guidance as to how such a mirror would be provided, optical fibers may be quite small in their diametrical dimension, handling of the fibers may be quite difficult. Positioning of the bend is also difficult because of the small size of many such fibers.
U.S. Pat. No. 3,819,250 dated June 25, 1974 to Kibler, discloses a technique for producing a low loss, small radius bend in an optical fiber by controlling the temperature of the fiber using a thermo-electric cooler which causes an increase in the difference between the index of refraction of the core and that of the cladding. After the bend is completed, the fiber returns to its normal temperature, and the conditions for low loss propagation are reestablished.
3. Objects of the Invention
One object of the invention is to provide an improved method for producing small radius bends in optical fibers.
Another object of the invention is to provide improved apparatus for producing bends in optical fibers.
A further object of the invention is to provide an improved method for producing bends in optical fibers which facilitates handling of the fibers during processing.
Still a further object of the invention is to provide an improved apparatus for handling optical fibers for bending the fibers, and providing a mirrored surface at the apex of the bend.
These and other objects and advantages of the invention will become apparent when considered in light of the following description and claims when taken together with the accompanying drawings.